1. Field of the Invention
The present invention relates to a semiconductor device. For example, the present invention relates to the arrangement of a power supply circuit that generates a voltage by using a bandgap reference circuit in a semiconductor memory device.
2. Description of the Related Art
A bandgap reference circuit is conventionally used as a voltage generator that generates a constant voltage. The bandgap reference circuit generates a physically constant voltage of about 1.25 V regardless of the temperature and the like.
Unfortunately, the conventional bandgap reference circuit has the problem that a normal operation becomes difficult to perform if the power supply voltage drops. If the power supply voltage, for example, becomes 1 V lower than 1.25 V, the bandgap reference circuit cannot generate 1.25 V, or becomes entirely inoperable.
Accordingly, a bandgap reference circuit having a variable output voltage is known (e.g., Jpn. Pat. Appln. KOKAI Publication No. 11-45125, to be referred to as a level variable bandgap reference circuit hereinafter). This arrangement can stably produce a voltage corresponding to the power supply voltage even if the power supply voltage drops. However, this circuit also has the problems that the circuit configuration is complicated, and the variation in output voltage is large.